Mix struct types in the same array

[tirithen]

On Thursday, 19 December 2019 at 00:00:56 UTC, Paul Backus wrote:
>
> interface Action
> {
>     void applyTo(ref User); <-- change to applyTo(T)(ref T)
> }
>
> class ActionAdapter(T) : Action
> {
>     T payload;
>
>     this(T payload)
>     {
>         this.payload = payload;
>     }
>
>     override void applyTo(ref User user) <-- change to 
> applyTo(U)(ref U entity)
>     {
>         payload.applyTo(user);
>     }
> }

Is there a way I can make the example a bit more generic even by 
replacing the User type with a template. I tried:

applyTo(ref User); <-- applyTo(T)(ref T)
applyTo(ref User user) <-- applyTo(U)(ref U entity)

It compiled but crashed with:

Linking...
/usr/bin/ld: 
.dub/build/application-debug-linux.posix-x86_64-dmd_2089-4CFAD9B3CA5E5532C5E0608F9332C781/tryit.o: in function `_Dmain':
.....tryit/source/app.d:55: undefined reference to 
`_D5plant5tryit3app5Event__T7applyToTSQBjQBgQBd4UserZQzMFKQvZv'
collect2: fel: ld returnerade avslutningsstatus 1

I'm still a bit new to this language so need to practice 
templates more, but I find D overall nice.